The invention relates to an arrangement for open-end rotor spinning having a spinning rotor which has a fiber sliding surface expanding conically to form a fiber collecting groove. The mouth of a fiber feeding duct is disposed opposite this fiber sliding surface. The fiber feeding duct starts at an opening roller and tapers toward the fiber sliding surface. A cover closes a rotor housing which is connected to a vacuum source which takes in an air current through the fiber feeding duct, the cover having a component in the form of an insert projecting into the spinning rotor. The fiber feeding duct is provided with at least one bypass opening at a distance from the mouth.
In order to ensure optimum spinning conditions, it should be ensured during open-end rotor spinning that the fibers transported in the air current in the fiber feeding duct reach the fiber sliding wall of the spinning rotor, on the one hand, at a sufficient distance from the open end of the spinning rotor and, on the other hand, also at a sufficient distance from the fiber collecting groove. By means of the distance from the open end of the spinning rotor, it is ensured that no fibers are taken along by the transport air flowing off over the open rotor edge. The distance from the fiber collecting groove provides that the fibers can still be stretched on the path taken on the fiber sliding surface leading to the fiber collecting groove. In the case of today's open-end rotor spinning machines, there is a tendency in the direction of progressively smaller spinning rotors so that it becomes more and more difficult to meet the above-mentioned requirements. It is therefore necessary to lead the fibers in a very targeted manner to a certain point of the fiber sliding surface of the spinning rotor which can be achieved mainly by a mouth of the fiber feeding duct with a small cross-section. In this case, there is the danger, however, that because of the small cross-section of the mouth, the amount of the taken-in air current will be reduced so that a perfect fiber transport is not ensured, and there is the additional risk that the opening roller is affected by the fly.
In order to solve the above-described problem, it is known from German patent document DE-37 04 460 Al to enlarge the mouth of the fiber feeding duct in the circumferential direction of the spinning rotor, but to keep it as small as possible transversely to it, i.e., in the axial direction of the spinning rotor.
For the same purpose, it is also known from German patent document DE-37 30 706 Al to open up the fiber feeding duct by means of a lateral slot in the end area opposite the fiber sliding surface so that the cross-section that is essential for the taken-in amount of air is transferred back to an area of the fiber feeding duct with a larger diameter.
It is also known from German patent document DE-31 20 877 Al to separate the transport air before it enters into the spinning rotor from the continuously flying fibers in order to remove fine dirt particles, particularly dust, before the entry into the spinning rotor. In the known construction, the fiber feeding duct, for that reason, is provided with large-surface openings in an area outside the spinning rotor through which the transport air is sucked off.
It is an object of the invention to develop an arrangement of the initially mentioned type in such a manner that a fiber feeding duct is made possible which has a mouth with a small cross-section without resulting in a reduction of the amount of air of the transport air current.
This object is achieved in that the at least one bypass opening has a smaller cross-section than the mouth of the fiber feeding duct and is situated at a point of the fiber feeding duct which has a larger cross-section than the mouth.
By means of this design, it is ensured that, on the one hand, the transport air current flows with a sufficient amount of air without the requirement of increasing the vacuum generated by the vacuum source. On the other hand, it is ensured that a sufficient amount of transport air also flows to the end of the fiber feeding duct and is discharged from the mouth. As a result of the relatively small bypass opening or bypass openings, it is also reliably prevented that fibers are sucked off through it or them. These bypass openings also have the result that the cross-section is enlarged which determines the taken-in amount of air at a given vacuum.
As a further development of preferred embodiments of the invention, it is provided that the sum of the cross-sections of the mouth and of the at least one bypass opening is no larger than the cross-section of the fiber feeding duct at the point of the bypass opening. As a result, it is achieved that the sum of the cross-sections of the mouth and of the bypass opening determine the taken-in amount of air so that it can be apportioned very precisely. In addition, it is also possible, by means of a corresponding dimensioning of the cross-sections of the bypass opening, to provide an overall intake opening which corresponds to the cross-section of the mouth of open-end spinning machines which are customary today and have had good results in practice.
In a further development of preferred embodiments of the invention, it is provided that the fiber feeding duct is provided with several bypass openings arranged symmetrically with respect to the longitudinal axis of the fiber feeding duct. This ensures that the flying direction of the fibers transported in the air current is disturbed as little as possible.